Kobako is an interesting thing. When you look at the bottle, you probably think "Opium imitator' -- after all, it's the same tall, flattened ovoid flask with a red top. And the juice has the same leather hints in base, spice-floral balancing routine, although Kobako moves more into the hairspray/floral than Opium.
But Kobako was created in 1938, and Opium came along in 1977!
Was Opium a copy/imitation of Kobako? Who can know. But Opium, Estee Lauder's Cinnabar, and Kobako all walk the same catwalk between spicy (cinnamon, pimento, ylang ylang), balsamic, and floral (jasmine, lily, rose), and all have a little bit of leather flourish in the base. And their roots can also be seen in L'Air du Temps and Patou's Divine Folie, in Coco and Tabac Blonde, and in latecomers Moschino and Jean Couturier's Keora.
Kobako is still kicking around various online sources and the bay, but I think it has probably been discontinued. It falls more into the floral line than its sisters, and the leather can feel a little more pronounced. While it can sometimes smell a teensy bit cheap (as some of the Bourjois reissues do), it's still quite lovely. I'm taking a lippie off for the slight bite of it, but it would be a half lippie if I could - Kobako is lovely and I wear it fairly often. It can pass in situations when Opium is just too lapel-grabbing and leg kicking.